CHAP. III.] 



BONE. 



21 



bony fibres or lamella, which in the cancellated texture join 

 and meet together so as to form a structure resembling lattice- 

 work (cancelli), and whence this tissue receives its name. In 

 the compact tissue these lamellse are usually arranged in close 

 rings around canals which carry blood-vessels in a longitu- 

 dinal direction through the bones. Between the lamellge are 

 branched cells which lie in cell-spaces or cavities called lacunce, 

 and running out in a 

 wheel - like or radial 

 direction from each la- 

 cuna are numerous tiny 

 canals or canaliculi 

 connecting one cell- 

 space or lacuna with 

 another, and forming a 

 system of minute inter- 

 communicating chan- 

 nels. 



All bones are cov- 

 ered by a vascular 

 fibrous membrane, the 

 periosteum, and, unlike 

 cartilage, the bones are 

 plentifully supplied 

 with blood. If we 

 strip this periosteum 

 from a fresh bone, 

 we see many bleeding ^ 14 ._T EA N S vE ESR SKCT.ON OF COMPACT 



points representing the TISSUE (OF HUMERUS). (Magnified about loOdiam- 



points at which the eterS - } ( Sha W->. Three of the Ha versian canals 

 r are seen, with their concentric rings faintly indi- 



blood- vessels penetrate cated ; also the lacunae, with the canaliculi extend- 



ing from them across the direction of the encircling 

 lamellae, or concentric rings. 



the bone. After en- 

 tering the bone the 

 blood runs through longitudinal channels which communicate 

 freely with one another, and are called, from the name of 

 their discoverer, Htiversian canals. Around these Haversian 

 canals, as we have already stated, the lamellse are disposed in 

 rings, while the lacunae containing the bone-cells are also 

 arranged, between the lamellse, in circles around the canals. 

 As the canaliculi run in a radial direction from the lacunse, it 



